In the past, various types of DC voltage regulators have been developed. DC voltage regulators normally receive a DC input voltage at a relatively high level and produce a DC output voltage at a lower level. The DC input voltage may be fluctuating, i.e., unregulated. Contrariwise, the output voltage is regulated, i.e., maintained at a predetermined potential level with respect to ground or some reference voltage.
One type of DC voltage regulator is the switching regulator. In a switching regulator a switch is turned on and off at a fixed or variable rate. With either a fixed or variable rate, the on-off time ratio of the switch is controlled such that the DC output voltage remains at a predetermined level as the source voltage or the load changes. Many prior art switching regulators do not include overload protection because, prior to the present invention, the inclusion of an adequate overload protection system in a switching-type regulator required complex output current sensing and control circuits. Yet, overload protection is desirable because a shorted regulator output or an exceedingly high load can draw current through the regulator switch (which is usually a semiconductor) greater than its rated value. In the absence of some form of overload protection, a short or an overload condition can damage or completely destroy the regulator. Simple fusing of such regulators is an unacceptable solution to this problem because the response time of fuses cannot be suitably matched to the protection requirements of semiconductor switching devices over the complete range of overload conditions.
Therefore, it is an object of this invention to provide a new and improved switching regulator.
It is a further object of this invention to provide an overload protected switching regulator.
In the past, as noted above, regulators have provided an output voltage regulated or referenced with respect to ground or some reference voltage level, frequently the regulator input voltage level. In other words, in one form of switching regulator, the regulator output voltage is regulated with respect to ground (zero voltage), whereas in the other form of switching regulator, the regulator output voltage is regulated with respect to some other voltage, such as the regulator input voltage. In either case, the differential voltage across the output of the switching regulator (i.e., the load voltage) is regulated. Obviously, it would be desirable to provide overload protected switching regulators useful in either of these environments.
Therefore, it is an object of this invention to provide an overload protected switching regular useful in systems wherein the output of the regulator is referenced to a zero voltage level (e.g., ground).
It is another object of this invention to provide an overload protected switching regulator useful in systems wherein the output of the regulator is referenced to a voltage level other than ground.
In addition to damage due to excessive current flow, switching regulators are also susceptible to thermal damage. While all of the components are susceptible to thermal damage, the regulator switch is particularly susceptible to such damage. For example, the high current flow passing through the switch when it is constantly loaded at or near its rated load produces heat. When the current generated heat is combined with the ambient heat surrounding the regulator, the resulting temperature may exceed the thermal limit of the regulation switch. In such cases, the regulator switch may be damaged or destroyed.
Thus, it is yet another object of this invention to provide a thermally protected switching regulator.
It is still another object of this invention to provide a switching regulator that is both overload and thermally protected.